Numerous systems have been developed for artificially producing snow wherein water and air under pressure are in some manner mixed and commingled. The principle involved is to reduce the size of water particles to the smallest size possible, typically by high pressure discharge of water through an atomizing nozzle orifice and augmented by injection of compressed air directly or indirectly with the water or mixing with air using deflectors and baffles within a mixing chamber.
Artificial snow is formed from seed crystals. Preferably, these seed crystals are formed from the expansion of compressed air expelled into the atmosphere within and around which minute water particles freeze and form artificial snow. The air, being compressed, is at a higher temperature than normal ambient winter air conditions and when expelled to ambient will expand to atmospheric pressure while simultaneously dropping greatly in temperature. Because of the refrigerating effect of such pressure reduction, if there is a high quantitative level of moisture vapor present in the compressed air, such moisture vapor upon expansion will condense, immediately forming seed crystals necessary for seeding atomized water spray particles for snow making. Of course, impingement of the expanding compressed air stream upon associated atomizing-spray-generated water particles also form such seed crystals. These seed crystals are immediately formed because of the extremely low temperature condition obtained through the expansion of the air together with the freezing effect of atmospheric conditions of winter, that is, temperatures below 32.degree. F. The seed crystals thus formed can be combined with the remaining water particles of the atomized water spray in a manner to form more artificial snow.
In connection with the atomizing of water for snow making, the water particle size should be as small as possible, because if such particles are too large, depending on ambient weather conditions and the ratio of water to air mixture, they will produce ice or sleet particles which are unsatisfactory for desirable skiing conditions. Also, the greater the water pressure at the discharge nozzle, the smaller the water particles or moisture droplets upon nozzle discharge.
There is no question that the most expensive operational cost component in any practical snow making system is the cost of generating the compressed air, which represents about 90 percent of the costs of consummables in the making of snow. In particular, compressor equipment necessary for an entire ski slope is very expensive to purchase and operate. Even in the face of these air compressor costs, it can be readily seen from the foregoing that these costs are further augmented by the efficiency loss of air pressure delivered to the system and discharged at the snow nozzles.
If these efficiency losses can be reduced in combination with a reduction of the amount of air pressure needed at the discharge nozzle, cost and operational expense of compressor and pump equipment can be substantially reduced while utilizing the pumping equipment of the snow making system at optimum efficiency levels. Air compressor costs cannot be eliminated, as compressed air is needed (except at very low ambient air temperatures and low humidity) because of the ability of the compressed air upon expansion into ambient to provide seed crystals. But these costs can at least be reduced through the optimum employment of equipment and the reduction of compressed air needed in snow making.
The art and science of producing artificial snow, or ice crystals physically resembling natural snow, has grown in importance over the last forty or so years with the increased interest in wintertime sports, most notably skiing. An accompanying concern in view of the vagaries of climatic conditions at the geographic location of most ski resorts is the ability to produce the maximum quantity, as well as quality, of artificial snow as efficiently as possible, particularly in view of the need to minimize the energy consumption per unit of artificial snow produced.
One of the earliest methods developed for producing artificial snow comprised mixing compressed air and water within a nozzle to effect particle formulation upon spraying of the internally-formed air/water particle mixture into the atmosphere at a temperature at or below freezing. Such a method and snow making "snow gun" is disclosed in Pierce, U.S. Pat. No. 2,676,471 issued in 1954. Although this Pierce snow gun method can cause snow crystals to be formed even at ambient air temperatures slightly above 32.degree. F., it nevertheless is operationally inefficient and consumes a considerable amount of energy. The Pierce snow maker "snow gun", which internally mixes compressed air with water within a spray nozzle, also is highly susceptible to nozzle clogging. Furthermore, such Pierce snow gun units depend upon the force of the compressed air to move the crystallized snow beyond the immediate area of the nozzle. The volume of compressed air required per unit volume of deposited snow is therefore quite high, resulting in poor energy utilization.
A substantial improvement over snow guns in making artificial snow was disclosed in Hanson U.S. Pat. No. 2,968,164 issued in 1962. Water droplets were sprayed directly into a high volume of moving air, at or below freezing temperature, which was generated by a platform-mounted fan. It was also found such snow formation could be improved by directing "seeding crystals", produced by combining compressed air and water internally in a spray nozzle (i.e., using a snow gun seeder), into the moving air flow into which the water droplets had been sprayed.
Following these basic Pierce and Hanson developments in the art, various improvements have been made, primarily in particular combinations and refinements in the manner in which seeding crystals are formed and injected, and how water droplets are introduced into a moving air-stream and the manner in which snow machines are constructed, mounted and elevated.
Thus in the late 1960's and early 1970s the Hanson-type of fan snow-making machine and method became commercially available in the form of fan-type snow making machines wherein a high-powered, electric-motor-driven fan, mounted within a cowling provided a substantially unidirectional high volume movement of air, and an array of water spray nozzles outside of the fan cowling provided water spray to be injected into the high volume movement at a rate and in a quantity sufficient to cause crystallization of the spray and deposition of the crystals as artificial snow. More particularly, Eustis et al U.S. Pat. Nos. 3,567,117; 3,703,991; and 3,733,029 disclosed such a snow making machine and method (sold commercially under the trademark "HEDCO".RTM.) whereby the fan generated movement of air directed from within a tunnel-like housing in which were provided both nozzles combining compressed air and water to form seeding crystals and a water nozzle. The related Dewey U.S. Pat. No. 3,948,442 disclosed a snow making machine with a motor-driven fan housed in a duct-like housing which also contained a nozzle for producing seeding crystals, while an array of water nozzles were provided in even distribution around the entire 360 degree circumference of the opening of the housing through which the airstream flows.
Another type of fan snow maker was disclosed in Ericson U.S. Pat. No. 3,610,527 wherein the atomizing technique involves movement of a film of water over the surfaces of a multi-blade fan, so as to effect improved evaporation and formation of snow without requiring use of compressed air for seeding or otherwise, this snow maker having been successfully commercialized under the trademark "SNOWSTREAM".RTM..
In the aforementioned HEDCO snow making machine constructed pursuant to the aforementioned Eustis et al. and Dewey patents a large fan is employed to move the crystallized snow beyond the area of the nozzle. However, compressed air and water are still internally mixed within one seeding (snow gun) nozzle and water is added to the fan-moved air by a second exterior nozzle. The seeding nozzles are disposed within the protective cowling of the fan, thereby resulting in additional difficulties in repairing clogged nozzles.
To overcome such problems, Everett Kircher invented (in early 1972) an improved fan snow maker as disclosed in Kircher U.S. Pat. No. 3,979,061. The Kircher '061 patent snow machine provided a dual array of nozzles surrounding the outside circumference of the opening of a duct within which a motor-driven fan generated an airstream. The inner array of nozzles injected high pressure water spray into the fan-propelled ambient air stream and the outer array of nozzles, arrayed individually in close proximity to each of the water nozzles, injected compressed air into the water spray of an adjacent water nozzle and also into the air stream. By so causing an "external" mixing in ambient of the expanding compressed air jet with an associated plume of water spray droplets, an increased volume of high quality snow is achieved by such plurality of water and air nozzles arrayed about the periphery of the high volume fan-propelled air flow movement. The respective nozzles are thus so disposed that each water spray is intersected and scattered by a high velocity air stream at the outer boundary of the main air movement. To achieve maximum scattering of water spray particles, the several high velocity air nozzles were spaced outwardly from the water spray nozzles so that the high velocity air streams convergently intersect the water sprays at relatively narrow acute angles tending to force the spray particles forward and into the center of the high volume air movement. The high velocity water spray and associated high velocity air stream are thus directed into a large volume air movement at first and second convergent angles with respect to the direction of movement thereof. The high velocity air stream intersects the water spray at a point remote from their respective nozzles to thereby achieve maximum dispersion of water particles throughout the unidirectional high volume air movement per unit volume of compressed air.
Thus an important feature provided by the Kircher '061 invention is preventing mixture of the water spray with high pressure compressed air until after both streams are in an unconfined state, i.e., "external" mixing and concurrent seed generation. This not only helps break up the water spray into finer particles, but also helps to better disperse the particles into and throughout the high volume movement of low pressure air in ambient atmosphere. Simultaneously, through the refrigeration effect of the rapidly expanding unconfined compressed air, seeding particles are generated at the point of intermixture of the water droplets of the air stream. Equally important, since there is no intermixture of air and water either within the nozzles or within the cowling, there is no chance for icing conditions to occur within any confined line, nozzle, passageway or the like. Hence the apparatus is relatively clog-free in operation.
As another feature, the Kircher '061 apparatus also eliminates the necessity of air and water pressure balancing in the respective air and water nozzle supply conduits, and thus permits maximum possible water pressure to be used at each individual snow machine. This is particularly advantageous in a down-hill line up of such machines fed from a common water supply hydrant system. Also, the greater the water pressure, the better the atomization of the water into fine particles of water. Consequently, less compressed air need be utilized in the snow making process if pressure balancing is not a factor. This results in the reduction of the amount of compressed air necessary in the snow making operation, thereby reducing the operational expense, in particular, of that element in the snow making operation which is the most expensive. Again, the '061 patent accomplishes this by not mixing the air directly with the water in a mixing chamber or within intercommunicating conduits in the machine per se, but rather by applying all compressed air externally (i.e., after it leaves the confines of its nozzle orifice and is unconfined in the ambient atmosphere) to similarly unconfined water fog produced after the high pressure water exits its water discharge nozzle. Also, the discharged air is directed to the throat of the water fog produced by the water nozzle.
Subsequently, the Dupre U.S. Pat. No. 3,822,825 apparatus utilized this '061 patent external air/water mix principle as applied to an array of air and water nozzles mounted at a high elevation on the upper end of an upright snow making water spray pipe tower. By so providing a compressed air nozzle adjacent and above a water atomizing nozzle for external mixing, as in the Kircher '061 patent invention and in the Dupre '825 patent, better snow making conditions can be obtained for two principal reasons. First, the compressed air, upon being expelled from the air nozzle into the atmosphere, is greatly reduced in temperature, causing it to give up its moisture in the form of seed crystals. These seed crystals form almost instantaneously. The air nozzle is positioned in a manner to be narrowly convergently directed into the throat of the water fog produced by the water nozzle to bombard as well as forwardly propel the water particles, which in many cases are as small as 200 microns or less, thereby uniting with these water particles to make snow particles or produce more seed crystals necessary in making snow.
It also should be understood that with all types of snow making apparatus "dwell time" is a critical parameter. In order to make artificial snow, the tiny atomized water particles need something to unite with other than falling through the ambient atmosphere. This is because of the surface tension of these minute water particles. Upon contact with one or more seed crystals, however, the surface tension of the water particles is broken and the unification of the seed crystal or crystals with the water particles will produce a multitude of snow flake-like crystals. This process continually occurs as the seed crystals and water particles intermingle during their fall to the ground. In this connection, it is important to provide for optimum conditions, which is governed by the best atomized spray possible to produce the smallest water particles as possible upon discharge, while not sacrificing the maximum distance or "throw" of discharge from the snow machine. Thus, optimum area of snow coverage is obtained, by providing maximum dwell time in which the seed crystals and tiny atomized water particles may completely commingle and unite to form snow prior to reaching the ground. Upwardly directed fan machines can accommodate these dwell time and throw factors fairly well with ground level mounting, but rather early on both snow guns and external mix and water nozzles were tower mounted in order to achieve such desirable dwell times.
Secondly, the expanding air from the air nozzle will help shred the atomized water particles into smaller and finer particles or droplets. This will permit the unification of many times more seed crystals with water particles for artificially forming snow skiing conditions.
In summary, in both external mix snow making fan and pipe tower apparatus, as well as in internal mix snow guns, the compressed air performs these functions; upon expansion:
1. it shreds the atomized water particles, either within or outside of the spray nozzle, into finer water particles; PA1 2. it implants seed crystals in the atomized water spray or fog; and PA1 3. it cools the entire discharge zone to an extremely cold condition highly desirable for snow making. This temperature at discharge has been known to be as low as minus 100.degree. F.
The Kircher '061 patent also discloses a "blow out" feature to dry the water conduit and spray nozzle system. After the water manifold is disconnected from the water source and the inlet aperture to the water manifold is opened to drain water therefrom, such blow out is accomplished by valving that directly connects the compressed air supply line leading to an air nozzle to an associated water nozzle such that a high velocity stream of compressed air is diverted from the air nozzle into the water nozzle and into water supply system of the snow machine, thereby driving the water from the system and preparing the water system for dry shut-down. That is, turning a three-way valve to the blow out position forces water in both directions from its point of entry into this valve so as to blow water out the ends of the water nozzles as well as to blow the water out of the water manifold via the open inlet. Hence, in a relatively short time, the water nozzles and the water manifold can be dried so that they do not freeze and clog during shut down.
The provision of the aforementioned low volume, high pressure air nozzles in snow making apparatus thus enables artificial snow to be made under adverse climatic conditions; i.e., when the dry bulb temperature is between 25.degree. and 32.degree. F. and the relative humidity between about 60 and 100 per cent. This result is believed to accrue from the aforementioned combined action of the refrigerating and dispersing effects of the high velocity, high pressure air stream.
Of course, as further pointed out in Kircher '061, when conditions are favorable for making artificial snow, as when the ambient air temperature is well below freezing, and the humidity is also low, the quantity of high pressure air can be cut down, i.e., the air/water ratio water-enriched, by reducing the number of compressed air nozzles in operation and even all entirely shut off, and good quality snow will still result merely from the mixture of water spray into the main air stream and ambient atmosphere. Conversely, as conditions worsen for producing artificial snow, the air/water ratio can be adjustably leaned out by having the additional air jets cut back into operation while the snow making machine continues in operation.
In this regard yet another feature of the paired three-way valving arrangement of the Kircher '061 patent is that it also enables the air/water ratio to be water-enriched by supplying high pressure water to any selected number of air nozzles to convert them to operate as additional water nozzles when conditions are very favorable to making snow; i.e., at the aforementioned very low temperature and humidity conditions when snow can be made with maximum discharge of water and a minimum amount of dispersion of water particles. This water "supercharging" feature thus further augments the flexibility of the apparatus of the Kircher '061 invention to meet a wide variety of snow making conditions.
It will be seen that this optional water supercharging use mode of additional water spray nozzles in the Kircher '061 patent snow making machine thus insures full utilization of the air discharged under pressure through the remaining open compressed air nozzle orifices that remain paired with associated water spray nozzles. By so discharging additional water under pressure through at least one additional water nozzle positioned adjacent to the first water nozzle which emits the spray interacting with the associated air jet stream, such that the additional water spray is directed into the resultant plume to interact therewith in ambient, the quantity of excellent quality snow produced may be greatly increased with the same compressed air consumption but without this addition of the extra "supercharging" water undesirably forming ice.
The foregoing "water supercharging" feature of the Kircher '061 patent was also subsequently applied to a rotatable and pivotable (universally manually adjustable) tower-supported snow gun array in the Tropeano et al U.S. Pat. No. 3,964,682. Likewise, in the Dupre U.S. Pat. No. 5,004,151 this water "supercharging" principle was applied to the earlier Dupre '825 patent external mix snow tower apparatus by providing additional water nozzles oriented to spray convergently into the ambient plume generated by paired air and water nozzles arrayed at the upper end of the snow tower.
It also has been long recognized as a general principle in the snow making art that the quantity of snow produced is a function of the amount of water used. However, under ambient air conditions of given temperature and humidity and for a particular rate of high-volume air movement, whether wind or fan-produced, only a limited amount of water may be sprayed onto the air movement and result in a high-quality, dry snow. Excess water may cause either a "dribble effect" with either fan-machines or snow making pipe towers or a deposit of undesirably wet snow, or both. Thus, there is a trade-off between snow quantity and quality for a given apparatus which varies in accordance with climatic conditions.
Accordingly, Hanson U.S. Pat. No. 4,004,732 added powered rotational and pivoting (oscillating) movement under an automatic control system to the Kircher '061 patent fan snow machine to better optimize snow making under varying climatic conditions. Then, as disclosed in Kircher et al U.S. Pat. No. 4,105,161, an improved and commercially successful method and fan-type snow making apparatus was made available (as sold under the trademarks "BOYNE SNOWMAKER".RTM. and "HIGHLANDER".RTM.) wherein the water nozzles are grouped in an accurate array entirely above the center line of the air stream and a deflector is used in combination therewith to direct a lower portion of the air stream upwardly toward these nozzles, for the purpose of reducing "dribble" and increasing the loft of the snow produced and propelled outward in the air stream. The Kircher et al '161 patent snow making machine also utilizes a seeding nozzle preferably cooperatively located within the "shadow" of the deflector to improve snow particle formation without re-introducing a dribble effect.
Of course, as indicated previously, it was also recognized early on in the snow making art that if the height of the snow maker above ground is increased, the quality of the snow increases due to the longer dwell time (the period of time from when the seed crystals are formed in the plume in front of the nucleator nozzles to the time that they reach the ground in the form of snow flakes). Thus, at least by the mid 1980's it was also common practice to elevate the aforementioned fan-type "BOYNE SNOWMAKER" and "HIGHLANDER" snow machine by tower mounting them, and likewise providing for pivotal (vertical plane) and rotational (horizontal plane) universal motion of these fan-type snow makers on their tower mounts.
Moreover, as early as in 1972, Dupre U.S. Pat. No. 3,706,414 disclosed a snow making system utilizing high snow pipe towers having discharge nozzles at the top of the tower that operated without fan-assist. Pressurized air and water are introduced at the bottom of each tower of the system where they are commingled to reduce the water into fine water particles which are discharged from the top of the tower approximately 35 feet above the ground and produce the seed crystals necessary to produce snow. The advantage obtained from this system is that, even without fan augmented dwell time, due to the tower height a characteristically long dwell time can be obtained, that is, the time between the time the seed crystals are formed upon discharge into the ambient atmosphere and the time the snow crystals, as formed from the seed crystals, finally settle upon the ground. Under suitable climatic conditions, this lengthy dwell time provides for sure and sufficient seed crystal formation of the atomized discharge as well as complete formation of good, well frozen snow crystals upon settling to the ground. Also, this system of high pipe snow towers does not usually interfere with recreational use of the ski slope, as skiers can use the slope while the snow making process is in progress. Further, a larger area of snow coverage can be efficiently obtained. Another advantage of pipe snow towers is low manufacturing cost and also reduced maintenance cost, in that once this snow making tower system is installed, little or no further maintenance costs will be incurred as the life of the system is as long as the life of the pipe employed in the system.
The later Dupre U.S. Pat. Nos. 3,822,825 and 3,952,949, in addition to utilizing the aforementioned Kircher '061 patent feature of external mix (in ambient) of compressed air and water spray to cause snow making "fog" at the top of the snow making tower, provided an improvement in such elevated snow making pipe towers by disposing the compressed air supply line within the water pipe that formed the tower so that the air line is isolated from the water line while at the same time it is protected from freezing ambient atmosphere by the surrounding water until the air reaches its discharge orifice to ambient at the top of tower.
Subsequently, the 1980 Dupre U.S. Pat. No. 4,199,103 provided a snow making pipe tower having the Dupre '825 patent features as well as greater "snow throwing" adjustability by providing a ground support pivot mount for the lower end of the snow making tower that also provided some rotational (swinging of the pipe in a horizontal plane) capability in addition to the swinging-in-a-vertical-plane pivotal adjustment capability. The later (1994) Dupre U.S. Pat. No. 5,360,163 improved the tower adjustment capability of the Dupre '103 patent adjustable snow making tower by detachably mounting the tower pipe on a support arm that is pivotally mounted on a rotatable support pipe that in turn telescoped onto a fixed ground support pole, and by manually adjusting the pivot angle of the tower pipe with a jackscrew coupled between the support tube and pivotal tower pipe, albeit generally in the manner of the manually and universally adjustable snow gun tower construction of the aforementioned Tropeano et al '682 patent.
Still another type of snow making apparatus known in the patented prior art, but apparently not commercially prevalent or practical, is represented by the U.S. patents to Ash U.S. Pat. No. 4,194,689; Fairbank U.S. Pat. No. 4,275,833; Rumney et al U.S. Pat. No. 4,813,597 and Werner U.s. Pat. No. 5,593,090. In general, the snow making devices disclosed in these patents employ a horizontally elongated piping array of side-by-side water spray nozzles either operating generally in manner of the aforementioned internal mix compressed air and water snow gun devices or, as in some vertical nozzle array pipe snow towers, with water spray nozzles alone augmented by chemical water supply snow making additives, and with the horizontal array being either stationary or rotatable and either ground or tower mounted.
In any event, it is well recognized in the snow making industry that the fan-type snow makers remain today as the most efficient commercially available means (in terms of operating costs) of producing artificial snow in quantity, particularly under adverse snow making conditions when snow is most needed, i.e., at elevated wet bulb temperatures (at least in the case of the aforementioned Kircher et al '161 patent fan-type machines). Nevertheless, the adjustable snow making pipe towers, as exemplified by the aforementioned Dupre patents, as well as portable single nozzle snow guns, remain less expensive to manufacture and maintain and thus can economically augment artificial snow making when snow making conditions are more favorable. Accordingly, in modern sophisticated snow making management as practiced at larger ski resorts today, there may be found a judicious operational mix of all three types of commercially prevalent snow makers, i.e., (1) single nozzle portable snow guns, as used primarily for limited bare spot and ski lift station "touch-up" throughout the ski season, (2) multiple-nozzle fan-type snow making machines (both ground and tower supported) for most economical operation under adverse snow making conditions to generate at high output the majority of artificial snow in building the pre-season and early season "base", and (3) the less expensive to manufacture and maintain, vertical array multiple nozzle type, snow making pipe towers (either fixed or adjustable mount) for cold weather snow making and thus primarily to augment mid-season snow production.